Cracks in blade

[Don K]

I'm using 1.25 10 degree blades on my LT 15 and noticed some small fractures  in the bottom of the gullets. These blades have not cut thousands of bdft like a hydraulic mill and has not had but one sharpening. I can tell when they start too because you can hear them on the blade guide rollers. One has broke already in the middle of the gullet in two places. I thought I would get much more use from these blades. And before you ask, WM blades, green to dry pine, poplar and yes I lube as needed and proper tension as the owner manual states. Any ideas?   Don

[Radar67]

Don, I thought about something after you left yesterday. The blades you are running for you LT15 are .042 right? With smaller band wheels, the .035 blades are better, but I have noticed they don't make them anymore. I read somewhere on the forum that the extra thickness could cause the stress cracks with the smaller band wheels.

Stew

[Furby]

Also, if your guides are not set right, you will get front to back flexing of the blade that will cause those cracks.
Make sure you blade is running about 1/8" off the back lip/edge of your guides when not in the cut.

[woodbowl]

I can tell when they start too because you can hear them on the blade guide rollers.

Don, is the back of the blade rubbing on the shoulder of the rollers when it's not in the cut? If so, it can cause cracks and breakage from the gullet side.

Furby's right about the gap between the back of the blade and the shoulder of the roller. Too large of a gap will cause cracks and breakage from the back side of the blade. Woodmizer recomends 1/16" on the power side and 1/8" on the idle side.

Make sure that both the idle and power sheeves are trackinging together on the same area of the blade. If the teeth are more forward on one pully than the other, it throws an imbalanced pressure on the band and can cause it to fail much quicker than normal. 

[Don K]

Thanks for the info so far. I did a alignment check per the owners manual when I first set the mill up. Everything looked good then, but I've had to move and reset up this mill about 4 times. I have not changed anything that I know of, but like car tires everything must have regular checks and realignments. I'm hoping to narrow the field down on possible causes. The mill is cutting as good as it did on day one and some of these things may not affect cutting quality just blade life. I will print this out for reference later this week when I am off as I have a big order of walnut and red cedar coming up. If ya'll can think of anything else please send it my way. We all know how expensive new blades are, I want to get as much use as possible.

Thanks, Don

[rewimmer]

Hello Don K,
I had a blade problem just after upgrading to a TK b-20 mill. What I found out was that I had a miss alignment problem and had assumed the mill was ok after just coming from the factory. After looking at the blades with a loop, I found cracks on the back side of the blade which was causing them to break. You could look down the length of the blade across the top of both band wheels and see a bow in the back of the blade before realignment. I used a good precession level , not the torpedo type that most people use, to align the mill properly. The orange box store carries the blue color levels and they are pricey. I leveled the bed of the mill and then leveled the drive wheel 90 deg to the bed. Then I leveled the idle band wheel  90 deg to the bed, then adjusted the tow in to get the blade tracking according to factory specs. Then set the guides and the problem went away. Also I am running 900 lbs of blade tension instead of the recommended 1200 lbs. This pressure was recommended by Timber Wolf and seems to be working great.
Robert in Virginia

[LT40HDD51]

In my experience, when the blade is rubbing against the flanges on the bg rollers it will crack from the back of the blade. There will also be a sharp, or rolled edge on the back too. Gullet cracks are usually caused by not grinding the gullet out completely every time. Small, microscopic cracks start to form in the bottom of the gullet, and proper grinding will remove them before they become a problem. If youre running them too hard between grinds these cracks become too big to remove with a regular grind, and the cracks will spread quite quickly...

Also, if the bg rollers are tilted too much in opposite directions, the blade is twisting back and fourth every time it goes around. Big time stress, this will eat blades like crazy. Ive been told by reliable sources that the blade running on that little roller is harder on it than making the bend around the blade wheel...

[Tom]

Things that cause cracks in the Gullet:

Pushing the blade too hard (Sawing too fast)
Sawing when the blade is dull (this is the most common problem)
Too tall of a tooth or anything that puts stress on the gullet.
Damage from a nail or uneven setting of teeth
Too much hook angle
A square Face to Gullet transition area
An unsmooth gullet (gouging when sharpening)
Not cleaning existing cracks from the gullet when you gum the blade.
Blade guides too far forward generally break the blade in the gullet and guides too far back cause cracks in the back of the body.

[LT40HDD51]

Ive been told by the WM blade guy that anything that rubs on the blade will crystallize the steel and start cracks. There have been issues with LT300s with the ceramic guide blocks under the blade too tight or on crooked and rubbing on the middle of the blade, and the blade would start to crack from the middle out. Same with the flanges rubbing on the back, crystallizes the back so it cant flex without fracturing. I saw WMs magnified pics of blades with different problems, along with a sample of the same blade. You can see the crystallization, with a microscopic crack (only a few thousandths long) starting at the worst spot. Cutting with a dull blade or pushing too hard will also push the blade back into the flange, giving the same problem.

[Tom]

I can't argue that crystalization isn't the problem, it makes sense, but the flange has a purpose.  It's to give beam strength to the portion of the blade that is in the cut.   If you aren't using it, you aren't getting the most from your mill.  That is why the distance between the flange and blade are critical.

[Robert Long]

Don K

Reading all that's been said, I too have 2 cents to add, but first some questions........
How long has the blade been cutting....1 hr, 2 hrs, 3 hrs. ?
How often do you sharpen them and do you sharpen them yourself?
What tension do you keep on them and are you forcing or pushing the blade (so to speak) through the cut?

For one thing, when you first "feel" that ripping in the gullet stop cutting and replace the blade and re-sharpen the blade to remove the fractures, this will restore live in the blade, sometimes I have to sharpen a blade 2 or 3 times to remove the fractures (look at them with a magnifying lens.

Tom has a good list of things to look for at the mill!

Robert

[MartyParsons]

Woood Mizer still makes a .035 blade. I would never run one on a LT15 unless that is the only blade available. We like the .045 on the LT15. The blades that comes with the LT15 is a .042. The advice the others above is right on.
1. 250 to 500 bd /ft per sharpening
2. You must grind the gullet when sharpening.
3. If you are following the 250 to 500 bd ft rule. Stop the blade when it is not in the wood cutting.
4. Cracks in the gullett are related to Flex life.
5. Cracks on the back of the blades usually come from the blade rubbing the shoulder of the blade or a wood chunk wedged in the saw.
6. Also rotate the B57 blets every 50 hours and check to see if there are any sap or bark stuck under the belt, causing the blade to flex. We also cehck the belt to see if any covering is missing cousing the same effect.
Some of these were covered in the other posts.
Marty

[Don K]

Robert, To answer your questions best I can. On the blade that I noticed the cracks in, on a manual mill , actual time in the wood maybe 3-4 hrs. This particular blade I believe has only been sharpened once. The tach on the motor only has about 55 hrs on it and I had 16 blades, so that doesn't put any given blade very much time on it. None of these blades have more than one sharpening. A fellow sawyer has a cooks sharpener and suffolk setter. Cams for all manufacturer of blades and degrees. 160+ blades a week. Not knocking Resharp, I've never used them so I have nothing to base this on, but he must be good enough to suit people. He has pulled several customers from Resharp and Cooks. I couldn't tell much if any difference on my mill between new blade and a sharpened one. Course you are talking manual mill.

I use manual tension according to WM specs for the LT 15 and I don't force the saw. My tach on the 15 Kolher runs about 3200-3300 all out and very rarely get below 2900 best I can tell because I saw by feel and engine sound and rarely look at the tach.

I thinking more of a mechanical thing than operator error. I have recieved some good info to check and will move on that and see what else comes up.    Thanks, Don

Marty posted before I could so I'll add that I've only sawed about 6000 bdft. Funny about 250 to 500 bdft rule because the instructors at the WM 25th class talked about the cost per blade relative to bdft cut. He said the more you can cut with that blade, more profit less cost between sharpenings. Of course Resharp states you can only get 2-3 sharpenings per blade as I guess they remove more during sharpening, which goes back to removing fracture. I seriously doubt I have more than 500 ft per blade.

Cracks are on the front of the blade and I have already rotated belts and remove them and clean the pulleys regularly. Marty you would like my mill I've had it two years and looks almost good as new, no missing parts, and only 3 small nicks. :D

[pineywoods]

Don, one question, are all the blades from the same box??? Good as WM's are, nobody's blades are perfect. I have had WM .045 blades break right out of the box.(new not resharp)
Try a different box of blades before you go adjusting on the mill. Ditto the previous posts, If you do your own, be sure to grind the gullet also. I must be an exception, I normally get at least 5 or 6 sharpenings per blade, some of them are shapened so many times, they get so narrow they won't track properly. I use a little more set and rake than recommended. Lest it sound like I'm bad-mouthing WM, there's no way. I've tried most of the various brands, and I'll stick with WM thank you.

[Radar67]

I've seen the blade Don is talking about. The cracks are not microscopic, there are easily recognized with the naked eye. I would estimate they are a sixteenth inch long and on at least every third gullet, right in the center, and run 90 degrees to the width of the blade. This blade looked fairly new and you could see the grinder marks in the gullets from the sharpening. They had a 10 degree angle on the tooth face and the set looked good on all the teeth. It may have been just a bad blade, the other one he had with him didn't have any cracks. Don did you check your other blades?

Stew

[Robert Long]

Don

Looks like we are all on the same track.......If you answered positively to all the questions and others have seen the blade in question I feel we have narrowed it down to a faulty blade.

Take down the information on the blade and call WM ( if it's a WM blade) they will or should honour the blade or give answers.   They can search their records on the lot to see if others have had problems on that same lot.

All the best with it and hope you get a satisfactory results ???

Robert

[mike_van]

One more thing to add - Always let the tension off the blade when you're done sawing - If i'm going off to do something else for a 1/2 hour, I back mine off.  Also, on my electric mill, I push the stop button at the end of the cut.  Just what I do, but i've got used to doing it, back the head up, set the depth, push start.  I get at least 6 sharpenings, sometimes 10 from .042 Red Streaks on 24" wheels.  When mine do go, it's cracks on the back of the blade.

[Don K]

The blades are in the same batch. I have not had time to check the others yet but I am as i don't want failure during the middle of a cut when my attention is focused on the music of sawing (you know the engine sound, blade singing through wood and all the other sounds that come with feeding your addiction). The sound of a failing blade is not good for the nerves or the heart when you are as close as I am cranking a LT 15. ;D  Happened one time already and I know it will happen again, but that don't mean I gotta like it.

I always release tension when the mill is down. I've gotten some good advice, that is why I posted and with ya'lls help I can work through it.    Don

[LT40HDD51]

I'd run em out and see what happens, providing you have your mill set up correctly. You cant worry about the blades breaking, almost all of mine end up dying by breaking in the middle of a cut (unless they meet something too hard  ;D). Keeps you on your toes  ;).

If it is a problem with the whole box breaking prematurely, Id send the numbers off the blades in to Wood-Mizer and see if they might have had problems with a batch or something...

[Don K]

I've checked all my blades and that one is the only one with the cracks besides the one that broke already. I will make a few checks on the mill tomorrow and see where I'm at. All from the same box but I doubt there is a issue with the blade quality. Thinking back on the life of this particular blade, it was the last one used on the mill and it cut 4 big 22"+ diameter 16' long dry pines, all cut into 1X12's for board and batten. I think this blade might have sacrificed itself for my workshop. :D :D    Don

[Robert Long]

Don K

I would still check the numbers on the blades in that box, the code numbers could be different and WM could have 2 or 3 different stock runs in the same box of blades.  Contact them, they are good people and will help with answers and perhaps a replacement would be in order.

Robert

[ely]

donk, i am not trying to brag here but when i sharpen a band on my sharpener it cuts way better than anything i have ever pulled out of a box. i have used a variety of bands have yet to pin down a definate preference yet. i quit counting the times i resharpen my bands after 10 or so. they started out as 1.25 bands and some of my old ones are getting down less than 1 1/8, dangerously close to the guide on my sharpener. i have thought bout adjusting my rollers up in the top holes on the sharpener to see how many more times i can sharpen them. having said that i do on occaision habve a band let go on my mill, it breaks in the gullet for reasons posted above. this has happened to me about 4 times in two years. i push things way pst there limit most times, some folks call me cheep i use the word frugal. ;D

[BBTom]

ely,

I believe you should be using the top hole for 1.25" bands.  The bottom hole is for 1.5" bands. 

I have gotten a few bands down close to 1" before they gave up.  I normally sharpen once or twice, then send back to resharp.  I don't like the way the bands cut after I set them.  I do not have enough patience to do a good job.  If the band is getting narrow, I will keep resharpening it till it just doesn't have enough set to run, then I scrap it. 

[ely]

i am not sure which hole i should be using. mine has 5 different holes to set the roller in. right now its in the middle holes. was there from the factory, i guess i could get the book out and check on it though.